Doubt in a COA problem

https://preview.redd.it/ne4pir2z57ag1.png?width=897&format=png&auto=webp&s=7e6e41a6451c6fb6b381c5d423269a3d61c08232

Link: https://gateoverflow.in/506798/go-classes-cs-2026-all-india-mock-test-2-question-17

My doubt is: How did we deduce/interpret that the number of tag addresses are candidates for a specific set ? I am not able to visualize and interpret. Any help or inputs are welcome.